Sewing machine speed control circuit

ABSTRACT

A sewing machine control circuit is disclosed in which acceleration or deceleration of the machine is effected by the operator in such a way as to gradually increase or decrease motor speed during periods of operator intervention and to maintain whatever speed exists at the time operator intervention ceases. Improved circuitry is utilized to perform these functions.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to an electric sewing machine. Namely, according to the invention, the rotation speed of the sewing machine is gradually accelerated up to a predetermined maximum speed by continuously operating one operating element. When the operating element is released on the way, the machine speed at the time is maintained. On the other hand, the speed is gradually reduced down to a certain minimum speed or until the sewing machine is stopped by continuously operating another operating element. Similarly when the operating element is released on the way, the machine speed at that time is maintained.

In the conventional pedal stepping speed control device of the sewing machine, a pedal stepping amount determines the speed of the sewing machine, and when the sewing operation is continued at a constant speed for a long time, the same stepping amount of the pedal has to be manually maintained. The portable sewing machines have recently been popularized and some of these machines are provided with a manual push button system in place of the pedal stepping speed control system. However, such a system is a very rough in actually selecting a desired speed, and if trying to select a desired speed, the operation is considerably difficult.

The present invention has been devised to eliminate the disadvantages in the prior art. It is a primary object of the invention to provide an electric sewing machine excellent in the speed control operation.

It is another object of the invention to easily and smoothly control the speed acceleration, the speed reduction and the maintenance thereof.

The other features and advantages of the invention will be apparent from the following description of the invention in reference to the preferred embodiment as shown in the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an outline of the sewing machine according to the invention,

FIGS. 2A and 2B show a control circuit diagram of the above,

FIG. 3-FIG. 6 show control signal waves in the circuit elements,

FIG. 7-FIG. 10 show the other embodiments of the above control circuits.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 of the drawings, a reference numeral 1 denotes a sewing machine. S_(F) is an operation switch for designating speed acceleration. While the switch is pressed, the rotation speed of the sewing machine gradually increases, and when it is released, the speed at that time is maintained. S_(L) is an operation switch for designating speed reduction. While the switch is pressed, the rotation speed of the sewing machine is gradually reduced, and when it is released, the speed at that time is maintained. S_(P) is a switch which is pressed to stop the rotation of the sewing machine.

In FIG. 2, a reference V is AC power source. M is a machine motor. TRIAC₁ is a two-way thyristor for controlling the speed of the motor, which is controlled of ignition phase by a pulse from a pulse transformer T. Numeral 2 is a speed designating circuit including an up-and-down counter COUNT₁ which produces the two-value code outputs A₄, A₃, A₂, A₁ designating a rotation speed of the sewing machine by operation of the switches S_(F), S_(L), S_(P). The counter COUNT₁ has the inputs I₁ -I₄ each connected to a positive power source Vcc via a pull-up resistor R₁. When the power source Vcc is supplied, a load terminal LOAD loads the inputs I₄, I₃, I₂, I₁ with a high level H, and renders all of the outputs A₄, A₃, A₂, A₁ a high level H. The four outputs at a high level H correspond to stopping the motor M, and those at a low level L correspond to the maximum speed of the motor M. Thus, the motor speed is controlled in correspondence to each number of 0 to 15 when the group of four outputs are considered in the decimal numbers. AM₁ is an oscillator producing a clock pulse in a constant period of e.g., 0.1 to 1 second, which is connected to a count-up terminal UP and to a count-down terminal DOWN of the counter COUNT₁ via NAND circuit NA₁ and NA₂ respectively, and its oscillating speed constitutes a speed for advancing or delaying the output code of the counter COUNT₁. FF₁ and FF₂ are D type flip-flop circuits respectively for designating the speed acceleration and the speed reduction, and each has a gate terminal Cp connected to the oscillator AM₁. The data terminals D are each switched over to the low level L by pushing the switches S_(F), S_(L) and are switched over to the high level H by releasing the switches. The complement side outputs Q are each connected to NA₁, NA₂. The speed acceleration switch is pushed to cause NAND circuit NA₁ to make effective the signal of the oscillator AM₁ to the DOWN terminal DOWN of the counter COUNT₁. The speed reduction switch is pushed to cause NAND circuit NA₂ to make the signal effective to the UP terminal UP. The OR circuit OR receives the four outputs from the counter COUNT₁ and gives them to NAND circuit NA₁. When the four outputs are all L, the OR circuit OR detects this and stops the DOWN input DOWN. When the four outputs are all H, the NAND circuit NA₃ detect this and stops the UP circuit UP via the NAND circuit NA₂. FF₃ is a D type flip-flop circuit having a gate terminal Cp connected to the oscillator AM₁ and having a data terminal D connected to the output of the NAND circuit NA₃, and having a complement side output Q which produces a signal of high level H for stopping the rotation of the motor M when the four signals are all at H of the counter COUNT₁. A reference numeral 3 is a pulse generating circuit for designating a motor speed, where an up-down counter COUNT₂ receives an encoded signal from the counter COUNT₁, and produces the output B₁ -B₄ which is rendered pulse width of the speed designation via a NOR circuit NOR₁ and are given for controlling the speed. AM₂ is an oscillator producing a clock-pulse in a period considerably faster than that of the oscillator AM₁. COUNT₃ is a binary counter of 12 stages, which receives a pulse from the oscillator AM₂ at its gate terminal Cp. The counter has a 4th stage output G₄ dividing said pulse into 1/16 of the period, and connected to the count-down terminal DOWN of the counter COUNT₂ via an inverter IN₂ and a NOR circuit NOR₃. The NOR circuit NOR₃ has an input terminal connected to the output of the NOR circuit NOR₁. When the outputs B₁ - B₄ of the counter COUNT₂ are all L, the NOR circuit NOR₃ is made inoperative to stop the COUNT-DOWN. The count-up terminal UP of the counter COUNT₂ is not used. A numeral 4 is a pulse generating circuit detecting the rotation speed of the sewing machine and producing a pulse in proportion to the rotation speed. SY is a speed detector producing symmetrical rectangular wave pulses of 23 periods per one rotation of an upper shaft of the sewing machine. A resistor R₂ and a capacitor C₁ compose a delay circuit. A signal wave of the speed detector SY and respective output waves of an inverter IN₄ and NAND circuit NA₄ receiving said signal wave make the output wave IN₄ of the potential of the capacitor C₁ as shown in FIG. 3 in which the lateral axis shows a time t. The output of the NAND circuit NA₄ is connected to the load terminal LOAD of the counter COUNT₂ so as to load the output A₁ -A₄ of the counter COUNT₁ at a rising point of the signal from the speed detector SY, and is further connected to the reset terminal RESET of the counter COUNT₃ via inverter IN₃ so as to reset the counter at a falling point of the signal from the speed detector. A numeral 5 is a comparator circuit which compares the speed designating pulse of the speed designating circuit 3 and the rotation speed pulse of the pulse generating circuit 4. When the rotation speed is faster than the predetermined speed, the comparator circuit 5 is operated to lower the potential of a non-inverting input terminal (+) of an amplifier OP₁ in order to delay the ignition phase of TRIAC₁. On the other hand, it is operated to raise the potential when the rotation speed is lower than the predetermined speed. AS₁ is an analog switch for controlling the reduction of rotation speed, and has a control input J₁ connected to the output of the NOR circuit NOR₁ via the NOR circuit NOR₄ and is also connected to the output of the inverter IN₄ through NAND circuit NA₅. When the control input J₁ is H, it discharges the load current of the capacitor C₂ via the resistor R₃. AS₂ is an analog circuit for controlling the acceleration of rotation speed, and has a control input J₂ connected through NOR circuit NOR₅ to an inverter output by an inverter IN₅ of the NOR circuit NOR₁ and is connected to an output of the speed controller SY through a NAND circuit NAND₆. When the control input J₂ is H, it charges the capacitor C₂ via the resistors R₃, R₄. The NAND circuit NA₅, NA₆ are connected to an output G₁₂ of a 12th stage of the counter COUNT₃ via the inverter IN₆ to make a stop control of the motor, and receive a pulse of the oscillator AM₂ divided in 1/4K period. When the oscillator AM₂ does not receive a reset signal on the way for an enough time, the terminal G₁₂ is made H and the NAND circuit NA₅, NA₆ are made inoperative. Then the operation of the counter COUNT₃ is stopped due to the output G₁₂ connected to another input of the NOR circuit NOR₂. A numeral 6 is a motor stopping circuit, in which PS is a needle position detector detecting the upper and lower dead point of the needle and generates a symmetrical rectangular wave pulse of a period in one rotation of the upper shaft of the sewing machine. The motor stopping circuit 6 receives the output Q of the flip-flop circuit FF₃ after the operation of the stopping switch S_(P) or after some continuous operation of the speed reduction switch S_(L), and receives the detecting signal of the needle position detector PS, and then stops the ignition of TRIAC₁, thereby to stop the sewing machine with a determined position of the needle. SR is a shift resistor having a gate terminal Cp connected to the output of the NAND circuit NA₄, and having a serial input SI which receives a signal from the needle position detector PS via an exclusive OR circuit ExOR which selectively determines the needle stopping position of the lower dead point. Then, the shift resistor SR produces from the 5-bit parallel output terminal an output as a signal of a phase delayed by 5 clock pulses. Ss is a switch for selecting the needle stop position at the upper dead point or at the lower dead point. The switch is closed to select the needle stop position at the upper dead point, and is opened to select the needle stop position at the upper dead point. FIG. 4 shows the output waves of the circuit elements, and the output wave of the needle position detector PS designates at the rising point the upper dead point of the needle and designates at the falling point the lower dead point of the needle. The signal is applied as a low level L to the exclusive OR circuit ExOR when the change-over switch Ss is closed, and is applied as a high level H to the exclusive OR circuit when the change-over switch Ss is opened. When the switch Ss is closed the output of the exclusive OR circuit ExOR is made the same phase with the signal of the needle position detector PS, and when the switch Ss is opened, the output signal is inverted. The output PO₅ of the shift resistor SR is a signal of a phase delayed by 5 pulses of speed detector signal SY with respect to the input ExOR. An AND circuit AND receives a signal of the exclusive OR circuit ExOR and a signal inverted by the inverter IN₇ of the output of the shift resistor SR. These signals are made effective only when the output Q of the flip-flop circuit FF₃ is H. Thus the AND circuit AND produces a signal having a width of 5 pulses of the speed detecting signal SY as shown in FIG. 4. AS₃ is an analog switch for controlling an initial rotation and controlling a re-rotation at a reduced speed of the machine when the stopping position of the machine is changed. The analog switch AS₃ has a control input J₃ connected to an output G₁₂ of the 12th stage of the counter COUNT₃. When the input J₃ is H, the inverted input by the inverter IN₈ from the AND circuit AND is made operative to charge the capacitor C₂ via the resistor R₅, R₃. A numeral 7 is a circuit to trigger the gate of the thyristor TRIAC₁. The trigger circuit 7 has a reset terminal connected to the output of AND circuit AND. When it receives a reset signal, it stops the operation of the pulse transformer T to stop the sewing machine. A reference 8 is a circuit producing saw-form waves, namely the waves OP- showing a power source phase to the power source V as shown in FIG. 5. The circuit 8 is connected to an inverting input terminal (-) of the amplifier OP₁ for comparing the phase angle. Thus, the circuit constitutes a reference for controlling the phase of the thyristor TRIAC₁. The output of the amplifier OP₁ is connected to a gate Cp of the trigger 7, and the rising phase of the pulse is an ignition phase of the thyristor TRIAC₁ for controlling the speed of the motor M.

In the above mentioned structure with reference to FIG. 2, when the power source V and the control power source Vcc are supplied, each of the outputs A₁ -A₄ of the counter COUNT₁ becomes H, and the output Q of the flip-flop circuit FF₃ becomes H. If this condition meets the stopping phase of the sewing machine based on the designation of the needle stopping position by the switch Ss, each of the inputs of the AND circuit AND becomes H, and the gate trigger circuit 7 is reset, and the sewing machine M is stopped at that phase (the case that the condition does not meet the stopping phase, will be described later).

Then the speed acceleration switch S_(F) is kept as it is pushed, the counter COUNT₁ counts down in the meantime with the operation period of the oscillator AM₁. Thus the value of the outputs A₄, A₃, A₂, A₁ is maintained when the switch S_(F) is released. At the initial counting down, the output Q of the flip-flop circuit FF₃ becomes low level L and the gate trigger circuit 7 is released from a reset condition. At this time, as the gate J₃ of the machine starting analog switch AS₃ becomes H during a certain stopping time of the sewing machine, the capacitor C₂ is charged via the resistor R₅, R₃. When the potential OP₁ + rises of the operation amplifier OP₁, for example, to the potential as shown in FIG. 5, the conductive wave of the thyristor TRIAC₁ which ignites at a crossing point with the potential PO₁ - becomes as shown in the solid lines with respect to the power source voltage including dotted lines (for the sake of simplifying explanation, it is assumed that the motor M is a loaded resistor), and the motor M starts rotation. Then, when the NAND circuit NA₄ generates a pulse as shown in FIG. 3, the counter COUNT₃ is reset and the output G₁₂ becomes L, and then the analog switch AS₃ is opened (OFF). At the same time, the counter COUNT₂ loads the speed designating signal A₁ -A₄. Since the signal includes H, the NOR circuit NOR₁ becomes L and the counter COUNT₂ starts counting down per pulse from the output G₄ of the counter COUNT₃. When a certain time passes, the outputs B₁ -B₄ become all L and the NOR circuit NOR₁ becomes L. The time from L to H becomes shorter, as shown by the pulse width D₁ -D₄ . . . in FIG. 6, as the code value of the speed designating signals A₁ -A₄ becomes smaller, that is, as the time of pushing the switch S_(F) becomes longer. Accordingly, the time ON of the speed acceleration analog switch AS₂ is increased to elevate the level OP₁ + in FIG. 5, and the crossing points between the level OP₁ + and the level OP₁ - move to the left in FIG. 5. As a result, the ignition angle of the thyristor TRIAC₁ is enlarged, and the rotation speed of the motor M is increased. In FIG. 6, the rotation speed SY of the sewing machine is constant, because as the rotation speed of the motor M increases, the period of the signal SY becomes shorter and the pulse width of the signal AS₂ becomes narrower to such a degree that the pulse is almost nonexistent, and the motor M is rotated at a designated constant speed.

When the speed reduction switch S_(L) is kept as it is pressed for a certain time, the counter COUNT₁ counts up and maintains the outputs A₄, A₃, A₂, A₁ at time of releasing the switch S_(L). With the time elapse of pressing the switch S_(L), that the pulse width becomes wider as shown by D'₁ -D'₄ in FIG. 6 to lengthen the ON time of the speed reduction analog switch AS₁. As a result, the level OP₁ + in FIG. 5 is lowered, and the rotation speed of the motor M is reduced. As the rotation is reduced, the pulse width of the signal AS₁ becomes narrower to such a degree that the pulse is almost nonexistent, and the motor M is rotated at a designated constant speed.

When the motor stopping switch S_(p) is pushed, the outputs A₁ -A₄ of the counter COUNT₁ become all H, and the reduction designating signal D'₁ -D'₄ becomes the maximum width, and the reduction analog switch AS₁ rapidly lowers the potential OP₁ + in FIG. 5. As a result the rotation speed of the motor M is rapidly reduced. As the motor is ready for stopping, the analog switch AS₁ becomes OFF. On the other hand, if the output Q of the flip-flop FF₃ is H due to the operation of the analog switch SP and the switch Ss is in a condition for stopping the needle at the upper dead point as shown in FIG. 2, the output of the AND circuit AND makes H per rising point of the signal from the needle position detector PS in the region between the predetermined rotation angles of the sewing machine in the same manner as the changeover switch Ss is ON in FIG. 4. In this high level period of the AND circuit, the gate trigger circuit 7 of the thyristor TRIAC₁ is reset and the driving torque of the motor M is made 0 in order to stop the motor in this period. However, in this case, if the rotation of the motor M does not yet reach the speed lower enough for stopping in this period, the sewing machine continues to rotate over this period due to inertia, and when the AND circuit AND becomes L, the gate trigger circuit 7 is released from the reset condition and the output G₁₂ of the counter COUNT₃ becomes H in the meantime. As a result, the analog switch AS₃ is ON to slightly elevate the (+) side level of the operation amplifier OP₁, thereby to re-rotate the motor M. As the motor speed is reduced enough, the motor M is stopped in the H period of the AND circuit AND in FIG. 4, that is, at the upper dead point of the needle. As this stopping time of the machine, the condition of the circuit elements is the same as they were when the power source was applied.

When the changeover switch Ss is made OFF in order to stop the sewing machine at the lower dead point of the needle, the H level phase of the AND circuit AND corresponds to the falling signal of the needle position detector PS as SsOFF in FIG. 4. As a result, the motor M is again driven and stops after 180° rotation of the sewing machine, i.e. at the lower dead point of the needle.

FIG. 7 shows another embodiment of the control circuit using an analog signal while the speed designating circuit 2 in FIG. 2 uses a digital signal. OP₂ is an operation amplifier having a non-inverting terminal (+) receiving a charged voltage of the capacitor C₃ as a speed designating input. R₆ is a semi-fixed resistor, one end of which is connected to the control power source Vcc, and constitutes an element through which the capacitor is charged with a time constant determined by the resistor and the capacity of the capacitor when the accelerating switch S'_(F) is closed. R₇ is a semi-fixed resistor one end of which is grounded, and constitutes an element through which said capacitor discharges with a time constant determined by the resistor and the capacity of the capacitor when the reduction designating switch S'_(L) is closed. S'_(P) is a motor stopping switch which is operated to directly and instantly discharge the capacitor without the need of resistor element. The inverting input terminal (-) of the operation amplifier OP₂ is connected to the output of the amplifier itself to constitute a voltage follower, and said output is connected to a voltage input type speed control circuit CONT to control the motor M. This voltage input type speed controlling circuits, for example as shown in FIG. 8, a light source LED of a photocoupler P.C receiving an output signal of the amplifier OP₂. In this case, the resistance value of a photo-conductor element CdS of the photocoupler is controlled, and the triac TRIAC₂ is phase-controlled via a diac DIAC to control the speed of the motor 4. C₄ is a resistor. If the output of the amplifier OP₂ is connected to, e.g., (+) side input of the amplifier OP₁ in FIG. 2, the voltage input type speed control circuit CONT in FIG. 7 can be composed of the amplifier OP₁ the gate trigger circuit 7, the saw wave producing circuit 8, the pulse transformer T, the triac TRIAC₁, to control the speed of the motor M.

FIG. 9 shows an embodiment which variably controls the resistance value for controlling the motor speed, while FIG. 2 and FIG. 7 disclose the embodiments which control the semi-conductors for controlling the motor speed. In this figure, MA is a control motor which reduces the value of the variable resistor R₈ during closing a speed acceleration switch S"_(F), and increases it during closing a speed reduction switch S"_(L) so as to accelerate or reduce the speed of the motor M. V+ and V- are a plus power source and a minus power source of the motor MA.

FIG. 10 shows a still another embodiment of a control circuit composed to drive the motor M with memorized set speed. The embodiment, instead of a stopping switch S'_(P) in FIG. 7, provides a capacitor C₅ charging the output of the operation amplifier OP₂ via the semi-fixed resistor R₉ and a memory starting switch S_(T) connected in parallel to the capacitor to charge and discharge the latter. Further, a non-inverting input terminal (+) of the operation amplifier OP₃ is so connected as to receive the charged voltage of the capacitor C₅. The output of the operation amplifier OP₃ is connected to the inverting terminal (-) of the same amplifier and constitute a voltage follower, and this output is also connected to the voltage input type speed control circuit CONT to control the motor M. The explanation is omitted to the parts common to those in FIG. 7.

In FIG. 10, if the memory starting switch S_(T) is opened, and the potential of the capacitor C₃ is determined by the speed acceleration designating switch S'_(F) and the speed reduction designating switch S'_(L) and then the potential of the capacitor C₅ is also determined, and the motor M is controlled in a speed designated by the switches S'_(F), S'_(L). In this condition, when the memory starting switch S_(T) is closed the capacitor C₅ is instantaneously discharged and the motor M is stopped. Further, when the memory starting switch S_(T) is opened, the output of the operation amplifier PO₂ charges the capacitor C₅ with a time constant determined by the resistor R₉ and the capacity of the capacitor C₅, and the output voltage of the amplifier OP₃ increases as the charged voltage increases, and the speed of the motor M gradually increases up to a speed designated by the switches S'_(F), S'_(L). The resistor R₉ may be adjusted slowly to increase the charged voltage so that the rotation of the motor M may be started slowly. 

We claim:
 1. A control circuit for use with electric motors and the like, particularly with electric motors in sewing machines, the circuit allowing a user to select a desired operating speed from a plurality of available operating speeds, and to vary such selected speed at will, the control circuit automatically causing the motor to maintain such desired operating speed until a user varies it comprising:a manually operable programmer producing a digital code signal which represents a desired operating speed, the programmer operating in a manner that the code signal produced can be varied to provide a plurality of codes corresponding to a plurality of available operating speeds and any code provided will be maintained until changed by a user; a clock pulse generator producing clock pulses of constant frequency; a clocked and programmable counter, the counter being connected to the programmer in order to be programmed thereby and being connected to the clock pulse generator in order to be clocked thereby and operating in a manner that when the counter is programmed with a code signal it will count one count away from the code signal each time the counter receives a clock pulse and will cease to count after counting to a predetermined number, the counter generating a digital drive signal, the drive signal having a first value when and only when the counter is counting and having a second value when and only when the counter has ceased to count, the counter further operating in a manner that it can always be reprogrammed with a code signal to begin counting again; a buffer responsive to the drive signal and producing an analog control signal, the control signal increasing when the drive signal has its second value and decreasing when the drive signal has its first value; a switch circuit in series with the motor, whereby the motor is turned on when the switch circuit is closed and whereby the motor is turned off when the switch circuit is opened; a switch control responsive to the analog signal and cooperating with the switch circuit in a manner that the switch circuit is closed and opened in response to changes of the analog signal; and a reprogram pulse generator responsive to position of the motor and cooperating with the counter, the reprogram pulse generator generating a reprogram pulse every time the motor rotates through a predetermined angle, whereby the counter is periodically reprogrammed with the code maintained by the programmer when such reprogramming occurs.
 2. The circuit defined by claim 1 wherein the programmer includes a binary counter with parallel outputs, a second clock pulse generator, a first pushbutton switch, a second pushbutton switch, and a third pushbutton switch all being connected together in a manner that the second clock pulse generator is connected to the binary counter to cause the counter to count down when the first pushbutton switch is closed, the second clock pulse generator is connected to the binary counter to cause the second binary counter to count up when the second pushbutton switch is closed, and the outputs of the counter are preset with a predetermined code signal when the third pushbutton switch is closed.
 3. The circuit defined by claim 2, wherein the binary counter has parallel inputs, and wherein the outputs of the binary counter are connected to the inputs of the programmable counter.
 4. The circuit defined by claim 1, wherein the analog control signal is derived from a voltage across a capacitor.
 5. The circuit defined by claim 1, wherein the switch circuit includes a triac in series with the motor.
 6. The circuit defined by claim 4 wherein the buffer includes an operational amplifier with an inverting input and a non-inverting input, a capacitor, and a sawtooth signal generator, the sawtooth signal generator being connected to the inverting input of the operational amplifier and the capacitor being connected between the non-inverting input of the operational amplifier and ground.
 7. The circuit defined by claim 3, wherein the binary counter has a minimum output and a maximum output, further including means for disconnecting the second clock pulse generator from the counter independently of the pushbutton switches, the means operating in such a manner as to prevent the counter from counting down after the minimum output has been reached and further to prevent the counter from counting up after the maximum output has been reached.
 8. The circuit defined by claims 1, 2, 3, 4, 5, 6, or 7, wherein the plurality of codes includes a code corresponding to a motor speed of zero.
 9. The circuit defined by claim 8, further including a stop monitor responsive to position of a motor driven element and cooperating with the switch control in a manner that when the code corresponding to a motor speed of zero is selected, the motor will continue to operate until the motor driven element has reached a predetermined position.
 10. The circuit defined by claim 9, wherein the stop monitor is adjustable to vary the predetermined position.
 11. The circuit defined by claim 8, further including a motor and a sewing machine driven by the motor. 